Update textbook.fr.md

12.temporary_ins/40.classical-mechanics/40.n4/70.lagrangian-mechanics/07.coherence/textbook.fr.md

@@ -174,11 +174,15 @@ $`\displaystyle\;=\int_{\alpha_1}^{\alpha_2}\dfrac{d (uv)}{d\alpha}\,d\alpha
 
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-$`\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i} \ cdot\delta \dpt{x}_i`$
+$`\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i} \cdot\delta \dpt{x}_i`$
 $`\;=\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot\dfrac{d x_i}{dt}`$
 
-$`\quad=\dfrac{d}{dt}\bigg({\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot x_i\bigg)
--\dfrac{d}{dt}\bigg({\partial\mathcal{L}}{\partial \dpt{x}_i}\bigg)\,x_i`$
+$`\quad=\dfrac{d}{dt}\bigg(\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot x_i\bigg)
+-\dfrac{d}{dt}\bigg(\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\bigg)\cdot x_i`$
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